The mosque is of great symbolic importance to both sides because Abu Bakr al-Baghdadi made his only public appearance as IS leader there days after the jihadist group proclaimed the creation of a “caliphate” exactly three years ago.

Image copyrightReuters

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Abu Bakr al-Baghdadi made his first public appearance as IS leader at the mosque in July 2014

The militants are now in retreat across Iraq and neighbouring Syria, where US-backed Kurdish and Arab fighters are laying siege to the city of Raqqa.

A coalition spokesman tweeted that some 84,000 sq km (32,000 sq miles) of territory had so far been retaken and more than four million people freed from IS rule, adding: “[IS’s] so-called caliphate is crumbling; from outside and from within”.

The research firm IHS Markit meanwhile estimated that the jihadists still controlled about 36,200 sq km (13,980 sq miles) across Iraq and Syria, and that their average monthly revenue had fallen dramatically, from $81m (£62m) in the second quarter of 2015 to $16m (£12m) in the second quarter of this year.

Image copyrightAFP

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The Iraqi military says all but 1 sq km (0.4 sq miles) of Mosul has been retaken

Iraqi pro-government forces launched an offensive to retake Mosul in October with air and ground support from a US-led multinational coalition.

They managed to take full control of the eastern half of the city in January and started an assault on the west the following month.

Only a few hundred militants are now believed to be left in about 1 sq km (0.4 sq miles) of the Old City, along with some 50,000 civilians who humanitarian organisations say have little food or water and are at great risk of injury or death.

BBC Arabic’s Feras Kilani says units from the Counter-Terrorism Service (CTS), Emergency Response Division (ERD), Federal Police and Iraqi Army began what they called the “final battle” for the Old City on Thursday.

The overall commander of the offensive, Lt Gen Abdul Amir Yarallah, swiftly declared that CTS troops had taken control of what remained of the Nuri mosque, as well as the Sirjkhana district.

But it was not until several hours later that troops entered the mosque complex, our correspondent says.

The Great Mosque was named after Nur al-Din Mahmoud Zangi – famous for mobilising and unifying Muslim forces to wage jihad against the Christian Crusaders – who ordered its construction in 1172, shortly before his death.

Media captionBlast in Iraq destroys Great Mosque of al-Nuri

Despite its connection to such an illustrious figure, all that remained of the original mosque was its leaning minaret – nicknamed “al-Hadba”, or “the humpback” – some columns and the mihrab, a niche indicating the direction of Mecca.

The Iraqi military said IS militants blew up the mosque and minaret eight days ago, leaving only the base of the minaret and a dome supported by a few pillars.

IS accused the US-led coalition aircraft of bombing the site, but experts said a video circulated online appeared to show charges inside the structures exploding.